Sorry to point this out. I notice for the game between Cronulla and Newtown at Endeavour Field on July 3, 1983.
-That you have Glen Mortimer Wearing No. 14.
-Mortimer Wore No. 20. When he came off the Bench for Cronulla in that game.
Source for this is:
https://www.youtube.com/watch?v=DPcy--CGyLA
Perhaps somebody can identify number 15 for Cronulla
I believe No. 15 is Steve Anderson.
After looking at the video I think Greg Nixon is #15.
Steve Anderson(#4) & Ian Forrest(#6) were originally selected at centre & 5/8 but neither started the game. Jersey #15 is on the field when Gardiner scored in the 4th minute so it must be Greg Nixon as John O'Connor(long blonde hair) is later seen in #4, Steve Anderson has much darker hair than O'Connor so it can't be him.
I can't spot #6 jersey in the clip so it looks like Nixon started the game at 5/8 in jersey #15, John O'Connor started the game in #4(originally allocated to Anderson) and Anderson is not seen in the clip as he came on the field after Glen Mortimer scored his try in the 75th minute.